public boolean contiansStudent(String ln)- given the last name of the student and determines if the student exists in the list.

public Student retrieveById(int id)- given the id, finds student in list and returns the student. If student not found, eturn null.

public int retrieveId(String ln)- given last name of student, return the id for that student.

public boolean addStudent(Student s)- adds the Student s to the list and true or false value that this was accomplished. This method should not allow duplicate students to be added (duplicate meaning same name or id).

public boolean removeStudent(int id)- removes a student from the list based on id.

public boolean removeStudent(String ln)- removes a student from the list based on last name.

public void printRoster()- print all students in the ArrayList<Student> list.